The object of this proposal is to enhance our limited understanding of the pathophysiology of autism spectrum disorders (ASDs), which is a devastating neurodevelopmental condition affecting 1 in 88 US children. This will be accomplished by studying human neurons induced from human embryonic stem cells (ESCs) that are conditionally knock out for neurexin-1 (Nrxn1), a gene that is frequently mutated in patients with ASDs. The synaptic role of Nrxn1 and its functional contribution to autism in human neuronal context has not been studied, which makes this study unique. Preliminary data indicates the feasibility of this approach, whereby ESCs conditionally mutant for Nrxn1 locus has been generated. Using these cells, human excitatory neurons will be generated whereby Nrxn1 gene will be conditionally knocked out during neuronal development. Based on the hypothesis that Nrxn1 is required for proper synaptic function in human neurons, I will compare synapse development and function (synaptic transmission) in control and Nrxn1 mutant human neurons. Nrxn1 function in synapse development will be monitored by morphological studies examining synapse density and size as well as synaptic vesicle cycling. Using, electrophysiolgical assays, I will assess both pre and postsynaptic functions of Nrxn1 in mediating synaptic transmission at human excitatory synapses. In total, these experiments attempt to determine the mechanism by which mutated Nrxn1 influence human synaptic transmission and as a consequence, contribute to autism, using a combination of experimental approaches that assess synaptic function. !